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Run-off formation in a humid, temperate headwater catchment using a combined hydrological, hydrochemical and isotopic approach (Jizera Mountains, Czech Republic)

Abstract:

The formation of baseflow and stormflow was examined in the 1.18km2 part of the headwater catchment Uhlířská, Jizera Mountains, Czech Republic, over the period 2007-2011, by means of run-off data and environmental tracers 18O and SiO2. The baseflow, computed using the digital filter approach BFLOW, contributes 67% to total streamflow and has a mean residence time of 12.3months. It is formed by groundwater discharge from the valley deluviofluvial granitic sediments, in combination with soil water in weathered layers on hillslopes during rainfall and snowmelt periods. The prevailing source of the groundwater is the infiltration of snowmelt water. Analysis of 20 run-off events and their hysteretic patterns demonstrated that the stormflow water has a residence time of about 4months and is generated by preferential flow on hillslopes combined by soil matrix drainage. Because of slower flow in the soil matrix, the enrichment of pore water in SiO2 is more pronounced. The stormflow and snowmelt water flowing via preferential pathways of upslope minerals soils pushes the pre-event groundwater through the pathways in wetlands to the stream, and the wetland can be therefore considered as groundwater supplied. This mechanism has been found to be typical for the groundwater-supplied headwater catchments of the Jizera Mountains and can be also assumed in other mountainous headwaters of the granitic massif in Central Europe. The main methodological contribution of this study are the residence time calculations stratified by baseflow and event flow, identifying run-off components of different travel times to streams and linking them with geochemical run-off sources. This achievement was possible because of a comprehensive dataset on hydrology, stable isotopes and silica hydrochemistry in all relevant run-off generation components. This concept indicates that a possible long-term change in snowmelt may affect the run-off regime of headwater catchments to climate or land-use changes. © 2013 John Wiley & Sons, Ltd.